JP6075713B2 - Cover glass for display - Google Patents

Description

  The present invention relates to a display cover glass, and more specifically, to a display cover glass that has high strength and efficiently absorbs ultraviolet rays and visible light having a short wavelength.

  In liquid crystal displays, LEDs (light emitting diodes) suitable for being thin and light are used as a backlight light source. Currently, a white light source is synthesized by a combination of a blue LED and a green phosphor, a yellow phosphor, a red phosphor, and the like, and three primary colors are produced through a color filter. In this method, the spectral intensity of blue light is relatively high, and short wavelength light is easily scattered. For this reason, harmful effects such as easy eye fatigue are pointed out. Further, when the intensity ratio between the blue light of the excitation light and the fluorescence wavelength-converted by the phosphor is changed due to deterioration of the phosphor or the like, there is a problem that the white balance is changed and the color tone is changed.

  In response to this problem, a white LED light source has been proposed in which the excitation light is changed to an ultraviolet LED, and the phosphors of the three primary colors of RGB are excited with the ultraviolet light. In this method, the white balance does not change, but when the excitation ultraviolet light reaches the eye through the display, the harmful effect becomes even greater than in the case of blue light. Therefore, in this case, a measure is required to prevent harmful ultraviolet rays from entering the eyes.

  By the way, recent liquid crystal displays have a tendency to adopt a touch panel system. In addition, a notebook PC or the like has a larger screen size than a tablet PC or the like.

JP 2007-99557 A

  At present, as a cover glass for a display, a chemically strengthened glass having a compressive stress layer on the surface is mainly used (for example, see Patent Document 1). However, this tempered glass does not have a function of shielding ultraviolet rays or short-wavelength visible rays harmful to the eyes.

  Therefore, the present invention has been made in view of the above problems, and its technical problem is to devise a cover glass having a compressive stress layer on the surface and a function of shielding ultraviolet rays and visible light having a short wavelength. That is.

As a result of various studies, the inventor conducted a strengthening treatment after introducing a predetermined amount of CeO ₂ into a specific glass composition, and when this was used for a cover glass for a display, the above technical problem was solved. The present invention is found and proposed as the present invention. That is, the display cover glass of the present invention is a display cover glass having a compressive stress layer on the surface thereof, and has a glass composition of mass% in terms of the following oxides, SiO ₂ 50 to 80%, Al ₂ O _3. 5 to 25%, B ₂ O ₃ 0.1 to 15%, Na ₂ O 1 to 20%, K ₂ O 0 to 10%, MgO 0.5 to 12%, CaO 0 to 10%, CeO ₂ 0. It is characterized by containing 5 to 3% (excluding 0.5%) , Fe ₂ O _{3 0 to} 0.05%, and TiO ₂ 0 to 0.05% . Here, "the following terms of oxide", for example, in the case of cerium oxide, not only cerium oxide present in the form of Ce ^4+, CeO ₂ on cerium oxide is also present that CeO ₂ in terms in the state of Ce ³⁺ (Other oxides are similarly based on the indicated oxide).

CeO ₂ exists as trivalent or tetravalent cerium ions in the glass. Trivalent and tetravalent cerium ions efficiently absorb light having a wavelength of 250 to 420 nm in the glass composition system according to the present invention. Thereby, when using 350-405 nm ultraviolet LED as a backlight light source, even if it reaches | attains a display surface, a part of excitation light is not absorbed by fluorescent substance, but is shielded with a cover glass. As a result, a situation in which part of the excitation light reaches the eyes of the person watching the display is prevented.

Display cover glass of the present invention is less 0.05% content of _Fe 2 _{O 3,} and TiO ₂ content Ru der 0.05% or less. If Fe ₂ O ₃ or TiO ₂ is introduced into the glass composition, the glass may be colored or the color tone may change, resulting in a problem that the screen becomes dark. In particular, when CeO ₂ and TiO ₂ coexist, they are colored yellow and are difficult to use for a display cover glass. Therefore, if the contents of Fe ₂ O ₃ and TiO ₂ are regulated as described above, such a problem can be easily prevented.

In the display cover glass of the present invention, it is preferable that the compressive stress layer has a compressive stress value of 100 MPa or more and the compressive stress layer has a stress depth of 10 μm or more. Since the display cover glass of the present invention contains CeO _{2 in the} glass composition, it has an effect of absorbing ultraviolet rays, and the glass composition is regulated to a predetermined range, so that compressive stress easily enters and the strength increases. It also has the effect. Here, the “compressive stress value of the compressive stress layer” and the “stress depth of the compressive stress layer” are observed when the sample is observed using a surface stress meter (for example, FSM-6000 manufactured by Toshiba Corporation). This is a value calculated from the number of interference fringes and their intervals.

  The display cover glass of the present invention preferably has a thickness of 0.3 to 1.0 mm. In this way, ultraviolet rays can be shielded while ensuring strength.

  The display cover glass of the present invention is preferably used for a liquid crystal display.

Reinforced glass of the present invention has a glass composition, in weight percent terms of _{oxide, SiO 2 50~80%, Al 2} O 3 5~25%, B 2 O 3 0.1 ~15%, Na 2 O 1-20%, K ₂ O 0-10%, MgO 0.5-12%, CaO 0-10%, CeO ₂ 0.5-3% (but not including 0.5%) , Fe ₂ It is characterized by containing O _{3 0 to} 0.05% and TiO ₂ 0 to 0.05% .

  The display cover glass of the present invention has a compressive stress layer on the surface thereof. As a method for forming a compressive stress layer on the surface, there are a physical strengthening method and a chemical strengthening method. The display cover glass of the present invention is preferably prepared by a chemical strengthening method.

  The chemical tempering method is a method for producing tempered glass by introducing alkali ions having a large ion radius to the surface by ion exchange treatment at a temperature below the strain point of glass. If the compressive stress layer is formed by the chemical strengthening method, the compressive stress layer can be properly formed even if the thickness of the strengthening glass is small. The tempered glass does not break easily like physical tempering methods such as cold tempering. Further, in order to prevent the tempered glass sheet from warping in the air cooling strengthening method, a thickness of 3 mm or more is necessary. be able to.

  The reason for limiting the content range of each component as described above in the display cover glass of the present invention will be described below. In addition, in description of the containing range of each component,% display points out the mass%.

SiO ₂ is a component that forms a network of glass, and its content is 50 to 80%, preferably 52 to 75%, 55 to 72%, 55 to 70%, particularly 55 to 67.5%. is there. If the content of SiO ₂ is too small, vitrification becomes difficult, and the thermal expansion coefficient becomes too high, so that the thermal shock resistance tends to decrease. On the other hand, if the content of SiO ₂ is too large, the meltability and moldability tend to be lowered, and the thermal expansion coefficient becomes too low to make it difficult to match the thermal expansion coefficient of the surrounding materials.

Al ₂ O ₃ is a component that enhances ion exchange performance, and is a component that enhances the strain point and Young's modulus, and its content is 5 to 25%. When the content of Al ₂ O ₃ is too small, resulting is a possibility which can not be sufficiently exhibited ion exchange performance. Therefore, a suitable lower limit range of Al ₂ O ₃ is 7% or more, 8% or more, 10% or more, particularly 12% or more. On the other hand, when the content of Al ₂ O ₃ is too large, devitrification crystal glass becomes easy to precipitate, the overflow down draw method, it becomes difficult to mold the glass sheet by a float method or the like. In addition, the thermal expansion coefficient becomes too low to make it difficult to match the thermal expansion coefficient of the surrounding material, and further, the high-temperature viscosity becomes high and the meltability tends to be lowered. Therefore, the preferable upper limit range of Al ₂ O ₃ is 22% or less, 20% or less, 18% or less, 17% or less, particularly 16% or less.

B ₂ O ₃ is a component that lowers the high temperature viscosity and density, stabilizes the glass, makes it difficult to precipitate crystals, and lowers the liquidus temperature. However, if the content of B ₂ O ₃ is too large, the ion exchange treatment may cause coloring of the surface called burnt, decrease in water resistance, decrease in the compressive stress value of the compressive stress layer, The stress depth of the stress layer tends to decrease. Therefore, the content of B ₂ O ₃ is 0.1 to 15%, preferably 0.1 to 13%, 0.1 to 12%, 0.1 to 11%, 0.1 to 6%, particularly 0.5 to 3%.

Na ₂ O is an ion exchange component, and is a component that lowers the high temperature viscosity and improves the meltability and moldability. Na ₂ O is also a component that improves devitrification resistance. The content of Na ₂ O is 1 to 20%. When Na 2 _O content is too small, or reduced meltability, lowered coefficient of thermal expansion tends to decrease the ion exchange performance. Therefore, when Na ₂ O is introduced, a preferable lower limit range of Na ₂ O is 10% or more, 11% or more, and particularly 12% or more. On the other hand, when the content of Na ₂ O is too large, the thermal expansion coefficient becomes too high, the thermal shock resistance is lowered, and it becomes difficult to match the thermal expansion coefficient of the surrounding materials. In addition, the strain point may be excessively lowered or the component balance of the glass composition may be lost, and the devitrification resistance may be deteriorated. Therefore, a preferable upper limit range of Na ₂ O is 17% or less, particularly 16% or less.

K ₂ O is a component that promotes ion exchange, and is a component that has a large effect of increasing the stress depth of the compressive stress layer among alkali metal oxides. Moreover, it is a component which reduces high temperature viscosity and improves a meltability and a moldability. Furthermore, it is also a component that improves devitrification resistance. The content of K ₂ O is 0 to 10%. When the content of K 2 _O is too large, the thermal expansion coefficient becomes too high, the thermal shock resistance becomes difficult to match or decreased, the thermal expansion coefficient with those of peripheral materials. Moreover, there is a tendency that the strain point is excessively lowered, the component balance of the glass composition is lacking, and the devitrification resistance is lowered. Therefore, the preferable upper limit range of K ₂ O is 8% or less, 6% or less, 4% or less, and particularly less than 2%.

CeO ₂ exists as trivalent or tetravalent cerium ions in the glass. Trivalent and tetravalent cerium ions efficiently absorb light having a wavelength of 250 to 420 nm in the glass composition system according to the present invention. The CeO ₂ content is more than 0.5 to 3%. When the content of CeO ₂ is too large, absorption by cerium ions spreads to 420nm or more wavelength range of visible light, the glass becomes so colored. Therefore, the preferable upper limit range of CeO ₂ is 2.5% or less, 2.2% or less, and particularly 2% or less. When the content of CeO ₂ is too small, the absorption of ultraviolet rays becomes insufficient. Therefore, the preferable lower limit range of CeO ₂ is 0.6% or more, 0.7% or more, particularly more than 0.8%.

  In addition to the above components, for example, the following components may be introduced.

Li ₂ O is an ion exchange component and a component that lowers the high-temperature viscosity and improves the meltability and moldability. It is also a component that increases Young's modulus. Furthermore, the effect of increasing the compressive stress value is large among alkali metal oxides. However, when the content of Li 2 _O is too large, and decreases the liquidus viscosity, it tends glass devitrified. In addition, the thermal expansion coefficient becomes too high, so that the thermal shock resistance is lowered or it is difficult to match the thermal expansion coefficient of the surrounding material. Furthermore, if the low-temperature viscosity is too low and stress relaxation is likely to occur, the compressive stress value may be reduced. Therefore, the content of Li ₂ O is preferably 0 to 3.5%, 0 to 2%, 0 to 1%, 0 to 0.5%, particularly 0 to 0.1%.

The preferred content of Li ₂ O + Na ₂ O + K ₂ O is 5-25%, 10-22%, 15-22%, especially 17-22%. When _{Li 2 O + Na 2 O +} K content of ₂ O is too small, the ion exchange performance and meltability is liable to decrease. On the other hand, if the content of Li ₂ O + Na ₂ O + K ₂ O is too large, the glass tends to be devitrified, the thermal expansion coefficient becomes too high, the thermal shock resistance decreases, and the heat of the surrounding materials It becomes difficult to match the expansion coefficient. In addition, the strain point may be excessively lowered, making it difficult to obtain a high compressive stress value. Furthermore, the viscosity in the vicinity of the liquidus temperature may decrease, making it difficult to ensure a high liquidus viscosity. “Li ₂ O + Na ₂ O + K ₂ O” is the total amount of Li ₂ O, Na ₂ O and K ₂ O.

MgO is a component that lowers the viscosity at high temperature, increases meltability and moldability, and increases the strain point and Young's modulus. Among alkaline earth metal oxides, MgO is a component that has a large effect of improving ion exchange performance. is there. However, when there is too much content of MgO, a density and a thermal expansion coefficient will become high easily, and it will become easy to devitrify glass. Therefore, the upper limit range of MgO is 12% or less, preferably 10% or less, 8% or less, 5% or less, especially 4%. Lower limit range M gO is 0.5% or more, preferably 1% or more, particularly 2% or more.

Compared with other components, CaO has a large effect of lowering the high temperature viscosity and improving the meltability and moldability, and increasing the strain point and Young's modulus without deteriorating devitrification resistance. The content of CaO is 0 to 10% . However, when there is too much content of CaO, a density and a thermal expansion coefficient will become high, the component balance of a glass composition will be missing, and it will become easy to devitrify glass on the contrary, or ion exchange performance will fall easily. Therefore, suitable content of CaO is 0 to 5%, 0 to 4%, 0.01 to 3%, particularly 0.1 to 2.5%.

  SrO is a component that lowers the high-temperature viscosity without increasing devitrification resistance, thereby increasing the meltability and moldability, and increasing the strain point and Young's modulus. When the content of SrO is too large, the density and thermal expansion coefficient increase, the ion exchange performance decreases, the glass composition component balance is lost, and the glass tends to devitrify. The suitable content range of SrO is 0 to 5%, 0 to 3%, 0 to 1%, particularly 0 to 0.1%.

  BaO is a component that lowers the high-temperature viscosity without increasing devitrification resistance, thereby improving the meltability and moldability, and increasing the strain point and Young's modulus. When there is too much content of BaO, a density and a thermal expansion coefficient will become high, an ion exchange performance will fall, or it lacks the component balance of a glass composition, and on the contrary, it becomes easy to devitrify glass. The suitable content range of BaO is 0 to 5%, 0 to 3%, 0 to 1%, particularly 0 to 0.1%.

  ZnO is a component that enhances the ion exchange performance, and is a component that is particularly effective in increasing the compressive stress value. Moreover, it is a component which reduces high temperature viscosity, without reducing low temperature viscosity. However, when the content of ZnO is too large, the glass tends to undergo phase separation, the devitrification resistance decreases, the density increases, and the stress depth of the compressive stress layer decreases. Therefore, the content of ZnO is preferably 0 to 6%, 0 to 5%, 0 to 1%, particularly preferably 0 to 0.5%.

ZrO ₂ is a component that remarkably improves the ion exchange performance, and is a component that increases the viscosity and strain point near the liquid phase viscosity. However, if its content is too large, the devitrification resistance may be significantly reduced. There is also a possibility that the density becomes too high. Therefore, the preferable upper limit range of ZrO ₂ is 10% or less, 8% or less, 6% or less, particularly 5% or less. When it is desired to improve the ion exchange performance, it is preferable to introduce ZrO ₂ into the glass composition. In this case, a suitable lower limit range of ZrO ₂ is 0.01% or more, 0.5%, 1% or more, 2 % Or more, particularly 4% or more.

P ₂ O ₅ is a component that enhances ion exchange performance, and in particular, a component that increases the stress depth of the compressive stress layer. However, when the content of P ₂ O ₅ is too large, easily glass phase separation. Therefore, the preferable upper limit range of P ₂ O ₅ is 10% or less, 8% or less, 6% or less, 4% or less, and particularly 2% or less.

As a fining agent, one or two or more selected from the group of As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , F, Cl, and SO ₃ (preferably a group of SnO ₂ , Cl, and SO ₃ ) 30,000 ppm (3%) may be introduced. The content of SnO ₂ + SO ₃ + Cl is preferably 0 to 10000 ppm, 50 to 5000 ppm, 80 to 4000 ppm, 100 to 3000 ppm, particularly 300 to 3000 ppm, from the viewpoint of accurately enjoying the clarification effect. Here, “SnO ₂ + SO ₃ + Cl” refers to the total amount of SnO ₂ , SO ₃ and Cl.

The preferred content range of SnO ₂ is 0 to 10000 ppm, 0 to 7000 ppm, especially 50 to 6000 ppm. The preferred content range of Cl is 0 to 1500 ppm, 0 to 1200 ppm, 0 to 800 ppm, 0 to 500 ppm, especially 50 to 300 ppm. It is. A suitable content range of SO ₃ is 0 to 1000 ppm, 0 to 800 ppm, particularly 10 to 500 ppm.

Rare earth oxides such as Nd ₂ O ₃ and La ₂ O ₃ are components that increase the Young's modulus, and are components that can be decolored to control the color of glass when a complementary color is added. However, the cost of the raw material itself is high, and if it is introduced in a large amount, the devitrification resistance tends to decrease. Therefore, the rare earth oxide content is preferably 4% or less, 3% or less, 2% or less, 1% or less, particularly 0.5% or less.

In the present invention, in consideration of environmental, substantially _{As 2 O 3, F, PbO} , preferably contains no _Bi 2 _{O 3.} Here, “substantially does not contain As ₂ O ₃ ” means that the glass component does not positively add As ₂ O ₃ but allows mixing at the impurity level. This means that the content of As ₂ O ₃ is less than 500 ppm. “Substantially free of F” means that F is not actively added as a glass component but is allowed to be mixed at an impurity level. Specifically, the content of F is less than 500 ppm. It points to something. “Substantially no PbO” means that although PbO is not actively added as a glass component, it is allowed to be mixed at an impurity level. Specifically, the PbO content is less than 500 ppm. It points to something. By "substantially free of Bi ₂ O _3", but not added actively Bi ₂ O ₃ as a glass component, a purpose to allow the case to be mixed with impurity levels, specifically, Bi ₂ It indicates that the content of O ₃ is less than 500 ppm.

A display cover glass of the present invention, by appropriately selecting a suitable content range of each component, Ru can der to identify suitable glass composition range.

The display cover glass of the present invention has a compressive stress layer on the surface. The compressive stress value of the compressive stress layer is preferably 100 MPa or more, 300 MPa or more, 400 MPa or more, 500 MPa or more, particularly 600 MPa or more. The greater the compressive stress value, the higher the strength of the cover glass. On the other hand, when an extremely large compressive stress is formed on the surface, microcracks may be generated on the surface, which may reduce the strength of the cover glass. In addition, the tensile stress inherent in the cover glass plate may be extremely high. For this reason, the compressive stress value of the compressive stress layer is preferably 1500 MPa or less. If the content of Al ₂ O ₃ , ZrO ₂ , MgO, ZnO in the glass composition is increased or the content of SrO, BaO is decreased, the compressive stress value tends to increase. Further, if the ion exchange time is shortened or the temperature of the ion exchange solution is lowered, the compressive stress value tends to increase.

The stress depth of the compressive stress layer is preferably 10 μm or more, 25 μm or more, 40 μm or more, particularly 45 μm or more. As the stress depth of the compressive stress layer increases, even if the cover glass is deeply scratched, the cover glass becomes difficult to break and the variation in strength becomes smaller. On the other hand, the greater the stress depth of the compressive stress layer, the harder it is to cut the tempered glass when producing the cover glass. For this reason, the stress depth of the compressive stress layer is preferably 500 μm or less, 200 μm or less, 150 μm or less, particularly 90 μm or less. Note that if the content of K ₂ O or P ₂ O _{5 in} the glass composition is increased or the content of SrO or BaO is decreased, the stress depth of the compressive stress layer tends to increase. Moreover, if the ion exchange time is lengthened or the temperature of the ion exchange solution is increased, the stress depth of the compressive stress layer tends to increase.

A display cover glass of the present invention, the density is preferably 2.6 g / cm ³ or less, in particular 2.55 g / cm ³ or less. The cover glass can be reduced in weight as the density is lower. In addition, the content of SiO ₂ , B ₂ O ₃ , P ₂ O _{5 in} the glass composition is increased, or the content of alkali metal oxide, alkaline earth metal oxide, ZnO, ZrO ₂ , TiO ₂ is decreased. As a result, the density tends to decrease.

Thermal expansion coefficient in a temperature range of 30 to 380 ° C. is preferably ^{40~120 × 10 -7 / ℃, 45~110} × 10 -7 / ℃, 50~110 × 10 -7 / ℃, especially 60 to 105 × 10 ⁻⁷ / ° C. If the thermal expansion coefficient is regulated within the above range, it becomes easy to match the thermal expansion coefficient of peripheral materials such as metals and organic adhesives, and it becomes easy to prevent peeling of peripheral materials such as metals and organic adhesives. If the content of alkali metal oxides and alkaline earth metal oxides in the glass composition is increased, the coefficient of thermal expansion tends to increase, and conversely the content of alkali metal oxides and alkaline earth metal oxides is reduced. If it decreases, the thermal expansion coefficient tends to decrease. Here, the “thermal expansion coefficient in the temperature range of 30 to 380 ° C.” can be measured by, for example, a dilatometer.

The strain point is preferably 500 ° C. or higher, 510 ° C. or higher, particularly 520 ° C. or higher. As the strain point is higher, the heat resistance is improved, and when the cover glass is heat-treated, the compressive stress layer is hardly lost. In addition, the higher the strain point, the less the stress relaxation occurs during the ion exchange treatment, and the easier it is to maintain the compressive stress value. If the content of alkaline earth metal oxide, Al ₂ O ₃ , ZrO ₂ , P ₂ O _{5 in} the glass composition is increased or the content of alkali metal oxide is reduced, the strain point becomes higher. easy. Here, the “strain point” is a value measured based on the method of ASTM C336.

The temperature at 10 ^4.0 dPa · s is preferably 1280 ° C. or lower, 1230 ° C. or lower, 1200 ° C. or lower, 1180 ° C. or lower, and particularly preferably 1160 ° C. or lower. As the temperature at 10 ^4.0 dPa · s is lower, the burden on the molding equipment is reduced, the life of the molding equipment is prolonged, and as a result, the manufacturing cost of the cover glass is easily reduced. If the content of alkali metal oxide, alkaline earth metal oxide, ZnO, B ₂ O ₃ , TiO ₂ is increased, or the content of SiO ₂ , Al ₂ O ₃ is decreased, 10 ^4.0 The temperature at dPa · s tends to decrease. Here, “temperature at 10 ^4.0 dPa · s” refers to a value measured by a platinum ball pulling method.

The temperature at 10 ^2.5 dPa · s is preferably 1620 ° C. or lower, 1550 ° C. or lower, 1530 ° C. or lower, 1500 ° C. or lower, particularly 1450 ° C. or lower. The lower the temperature at 10 ^2.5 dPa · s, the lower the temperature melting becomes possible, and the burden on glass production equipment such as a melting kiln is reduced, and the bubble quality is easily improved. That is, the lower the temperature at 10 ^2.5 dPa · s, the easier it is to reduce the manufacturing cost of the cover glass. The temperature at 10 ^2.5 dPa · s corresponds to the melting temperature. Also, if the content of alkali metal oxide, alkaline earth metal oxide, ZnO, B ₂ O ₃ , TiO _{2 in} the glass composition is increased or the content of SiO ₂ , Al ₂ O ₃ is reduced, The temperature at 10 ^2.5 dPa · s tends to decrease. Here, “temperature at 10 ^2.5 dPa · s” refers to a value measured by a platinum ball pulling method.

The liquidus temperature is preferably 1100 ° C. or lower, 1050 ° C. or lower, 1000 ° C. or lower, 950 ° C. or lower, 900 ° C. or lower, and particularly preferably 880 ° C. or lower. In addition, devitrification resistance and a moldability improve, so that liquidus temperature is low. In addition, increase the content of Na ₂ O, K ₂ O, B ₂ O _{3 in} the glass composition or decrease the content of Al ₂ O ₃ , Li ₂ O, MgO, ZnO, TiO ₂ , ZrO _2. In this case, the liquidus temperature tends to decrease. Here, the “liquid phase temperature” is obtained by passing a standard sieve 30 mesh (a sieve opening of 500 μm) and putting glass powder remaining in a 50 mesh (a sieve opening of 300 μm) in a platinum boat, and then in a temperature gradient furnace. This is a value obtained by measuring the temperature at which the crystals are deposited while maintaining the time.

The liquid phase viscosity is preferably 10 ^4.0 dPa · s or more, 10 ^4.4 dPa · s or more, 10 ^4.8 dPa · s or more, 10 ^5.0 dPa · s or more, 10 ^5.4 dPa · s or more. The above is 10 ^5.6 dPa · s or more, 10 ^6.0 dPa · s or more, 10 ^6.2 dPa · s or more, particularly 10 ^6.3 dPa · s or more. In addition, devitrification resistance and a moldability improve, so that liquid phase viscosity is high. Also, if the content of Na ₂ O, K ₂ O in the glass composition is increased or the content of Al ₂ O ₃ , Li ₂ O, MgO, ZnO, TiO ₂ , ZrO ₂ is reduced, the liquidus viscosity Tends to be high. Here, “liquid phase viscosity” refers to a value obtained by measuring the viscosity of glass at the liquid phase temperature by a platinum ball pulling method.

beta-OH value 0.5 mm ^-1 or less, 0.4 mm ^-1 or less, 0.3 mm ^-1 or less, 0.28 mm ^-1 or less, 0.25 mm ^-1 or less, particularly 0.22 mm ^-1 or less. The smaller the β-OH value, the better the ion exchange performance.

Here, “β-OH value” refers to a value obtained by measuring the transmittance of glass using FT-IR and using the following equation.
β-OH value = (1 / X) log (T ₁ / T ₂ )
X: Sample thickness (mm)
T ₁ : Transmittance (%) at a reference wavelength of 3846 cm ⁻¹
T ₂ : Minimum transmittance (%) in the vicinity of a hydroxyl group absorption wavelength of 3600 cm ⁻¹

(1) Select a raw material with a low water content, (2) Do not add moisture to the raw material, (3) Increase the amount of components (Cl, SO ₃ etc.) that reduce the moisture content, (4) In the furnace Reduce the moisture content in the atmosphere, (5) N ₂ bubbling in the molten glass, (6) Adopt a small melting furnace, or (7) Increase the flow rate of the molten glass, the β-OH value decreases Become.

  In the display cover glass of the present invention, the thickness (in the case of a plate shape) is preferably 1.0 mm or less, 0.8 mm or less, particularly 0.7 mm or less. If the thickness is too large, the mass of the cover glass will increase, so the mass of the display will increase and the portability will decrease. On the other hand, when the thickness is too small, it is difficult to obtain a desired strength. Therefore, the thickness is preferably 0.2 mm or more, 0.3 mm or more, particularly 0.4 mm or more.

  The transmittance at a wavelength of 350 nm is preferably 50% or less (desirably 40% or less, particularly 35% or less) with a thickness of 0.9 mm. If the transmittance at a wavelength of 350 nm is too high, it is difficult to ensure the ability to shield ultraviolet rays. The transmittance at a wavelength of 500 nm is preferably 80% or more (desirably 83% or more, particularly 85% or more) at a thickness of 0.9 mm. If the transmittance at a wavelength of 500 nm is too low, the visibility of the display tends to be lowered. The transmittance can be measured by a conventional method. For example, the measurement apparatus uses UV-3100PC (manufactured by Shimadzu Corporation), slit width: 2.0 nm, scan speed: medium speed, sampling pitch: 0.5 nm It can be measured under the following conditions.

  In the display cover glass of the present invention, it is preferable that a part or all of the edge region where the cut surface of the cover glass intersects the surface is chamfered, and at least a part of the edge region on the display side or It is preferable that the entire surface is chamfered. As the chamfering, R chamfering is preferable. In this case, R chamfering with a radius of curvature of 0.05 to 0.5 mm is preferable. Further, C chamfering of 0.05 to 0.5 mm is also suitable. Furthermore, the surface roughness Ra of the chamfered surface is preferably 1 nm or less, 0.7 nm or less, 0.5 nm or less, and particularly preferably 0.3 nm or less. In this way, it becomes easy to prevent cracks starting from the edge region. Here, “surface roughness Ra” refers to a value measured by a method based on JIS B0601: 2001.

Reinforced glass of the invention, as a glass composition, by mass% terms of _{oxide, SiO 2 50~80%, Al 2} O 3 5~25%, B 2 O 3 0.1 ~15%, Na 2 O 1-20%, K ₂ O 0-10%, MgO 0.5-12%, CaO 0-10%, CeO ₂ 0.5-3% (but not including 0.5%) , Fe ₂ It is characterized by containing O _{3 0 to} 0.05% and TiO ₂ 0 to 0.05% . The suitable glass composition, glass characteristics and the like of the tempered glass of the present invention have already been described in the explanation column of the display cover glass of the present invention, and detailed description thereof will be omitted here.

When the tempered glass of the present invention is subjected to ion exchange treatment for 4 hours in KNO ₃ molten salt at 430 ° C., the compressive stress value of the compressive stress layer on the surface is 100 MPa or more, and the stress depth of the compressive stress layer is Preferably, the compressive stress layer has a compressive stress value of 200 MPa or more, and the compressive stress layer preferably has a stress depth of 20 μm or more. Particularly, the compressive stress layer has a compressive stress value of 600 MPa or more, and The stress depth of the compressive stress layer is preferably 40 μm or more.

In the ion exchange treatment, the temperature of the KNO ₃ molten salt is preferably 400 to 550 ° C., and the ion exchange time is preferably 2 to 10 hours, particularly 4 to 8 hours. If it does in this way, it will become easy to form a compressive stress layer appropriately. Incidentally, the reinforcing glass of the present invention has a glass composition described above, without using a mixture of KNO ₃ molten salt and NaNO ₃ molten salt, increasing the compression stress value and stress depth of the compression stress layer can do.

  The glass for strengthening of the present invention and the cover glass for display (tempered glass) can be produced as follows.

  First, the glass raw material prepared so as to have the above glass composition is put into a continuous melting furnace, heated and melted at 1500 to 1600 ° C., clarified, then supplied to a forming apparatus, formed into a plate shape, etc. The glass for reinforcement | strengthening can be produced by cooling.

  As a method of forming into a plate shape, it is preferable to employ an overflow down draw method. The overflow downdraw method is a method that can produce a large amount of glass plates at low cost and can easily produce a large glass plate.

  In addition to the overflow downdraw method, various molding methods can be employed. For example, a forming method such as a float method, a downdraw method (slot down method, redraw method, etc.), a rollout method, a press method, or the like can be employed.

  Next, tempered glass can be produced by tempering the obtained tempered glass. The time when the tempered glass is cut into a predetermined dimension may be before the tempering treatment, but it is advantageous from the viewpoint of cost to carry out after the tempering treatment.

As the reinforcing treatment, an ion exchange treatment is preferable. The conditions for the ion exchange treatment are not particularly limited, and the optimum conditions may be selected in consideration of the viscosity characteristics, application, thickness, internal tensile stress, and the like of the tempered glass. For example, the ion exchange treatment can be performed by immersing glass in KNO ₃ molten salt at 400 to 550 ° C. for 1 to 8 hours. In particular, when K ions in KNO ₃ molten salt are ion exchanged with Na components in glass, a compressive stress layer can be efficiently formed on the surface.

  Hereinafter, the present invention will be described based on examples. The following examples are merely illustrative. The present invention is not limited to the following examples.

Table 1 shows Sample No. 1 to 5 are shown.

  Each sample in the table was prepared as follows. First, glass raw materials were prepared so as to have the glass composition in the table, and were melted at 1580 ° C. for 8 hours using a platinum pot. Thereafter, the obtained molten glass was poured out on a carbon plate and formed into a plate shape. Various characteristics were evaluated about the obtained glass plate.

  The density is a value measured by a well-known Archimedes method.

  A thermal expansion coefficient is the value which measured the average thermal expansion coefficient in the temperature range of 30-380 degreeC using the dilatometer.

  The strain point and annealing point are values measured based on the method of ASTM C336.

  The softening point is a value measured based on the method of ASTM C338.

The temperatures at 10 ^4.0 dPa · s, 10 ^3.0 dPa · s, and 10 ^2.5 dPa · s are values measured by a platinum ball pulling method.

  The liquidus temperature passes through a standard sieve 30 mesh (a sieve opening of 500 μm), puts the glass powder remaining in 50 mesh (a sieve opening of 300 μm) in a platinum boat, and holds it in a temperature gradient furnace for 24 hours. This is a value obtained by measuring the temperature at which crystals precipitate.

As is clear from Table 1, sample No. 1-4 have a density of 2.52 g / cm ³ or less and a thermal expansion coefficient of 61 to 99 × 10 ⁻⁷ / ° C., and were suitable as a material for tempered glass, that is, tempered glass. Moreover, since the temperature at 10 ^4.0 dPa · s is 1105 ° C. or less, the burden on the molding equipment is light, and the temperature at 10 ^2.5 dPa · s is 1480 ° C. or less, so that productivity is high and a large amount of It is considered that a glass plate can be produced at low cost. In addition, although the glass composition in a glass surface layer differs microscopically before and after ion-exchange treatment, when it sees as the whole glass, a glass composition does not differ substantially.

Next, each sample was immersed in KNO ₃ molten salt at 430 ° C. for 4 hours to perform ion exchange treatment, and then the surface of each sample was washed. Subsequently, the compressive stress value and stress depth of the compressive stress layer on the surface were calculated from the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval between the interference fringes. In the calculation, the refractive index of each sample was 1.52, and the optical elastic constant was 28 [(nm / cm) / MPa].

  As is clear from Table 1, sample No. 1 to 4 had a compressive stress value of 680 MPa or more and a stress depth of 15 μm or more.

The ultraviolet shielding ability was evaluated with a transmittance of 350 nm, and the visible light transmission property was evaluated with a transmittance of 500 nm. The measurement device used was UV-3100PC (manufactured by Shimadzu Corporation), and the measurement was performed with slit width: 2.0 nm, scan speed: medium speed, and sampling pitch: 0.5 nm.

  As is clear from Table 1, sample No. 1-4 were 5-32% in the range whose transmittance | permeability of wavelength 350nm is thickness 0.5-0.9mm. Sample No. No. 5 had a transmittance of 350 nm at a thickness of 0.9 mm and was 86%, and its ultraviolet shielding ability was low. Sample No. 1 to 5 all had high transmittance at a wavelength of 500 nm.

Claims (6)

A cover glass for a display having a compressive stress layer on the surface, as a glass composition, in weight percent terms of _{oxide, SiO 2 50~80%, Al 2} O 3 5~25%, B 2 O 3 0. _{1 ~15%, Na 2 O 1~20} %, K 2 O 0~10%, MgO 0.5~12%, CaO 0~10%, CeO 2 0.5~3% ( however, 0.5% ₂ ) , Fe ₂ O _{3 0 to} 0.05%, and TiO ₂ 0 to 0.05% . The display cover glass according to claim 1, wherein the content of K ₂ O is less than 2% .   The display cover glass according to claim 1, wherein the compressive stress value of the compressive stress layer is 100 MPa or more, and the stress depth of the compressive stress layer is 10 μm or more.   Thickness is 0.3-1.0 mm, The cover glass for a display as described in any one of Claims 1-3 characterized by the above-mentioned.   It uses for a liquid crystal display, The cover glass for a display as described in any one of Claims 1-4 characterized by the above-mentioned. As a glass composition, in weight percent terms of _{oxide, SiO 2 50~80%, Al 2} O 3 5~25%, B 2 O 3 0.1 ~15%, Na 2 O 1~20%, K 2 O 0-10%, MgO 0.5-12%, CaO 0-10%, CeO ₂ 0.5-3% (excluding 0.5%) , Fe ₂ O ₃ 0-0.05% Tempered glass containing TiO ₂ 0-0.05% .